Zirconia induction furnace

Abstract

A high frequency induction furnace (10) for reflowing a portion of a lightguide preform (44) in order to draw a fiber (52) therefrom. The furnace (10) has a centrally located tubular susceptor (34) therein having a thin coating of the preform material (e.g., silica) on at least a portion of the inside surface thereof. A cylinder (62) is positioned in concentric, spaced relation about the susceptor (34) and is surrounded by an insulating grain (36). A high frequency coil (38) is energized to couple its electromagnetic field to the susceptor (34) to heat and reflow a portion of the preform (44) in order to draw the fiber (52) therefrom. The thin coating prevents contaminating particulates from migrating from small cracks in the inside surface of the susceptor (34) onto the preform (44) while the cylinder (62) prevents small particulate emanating from the insulating grain (36) from being drawn through larger cracks in the susceptor and onto the preform and/or the fiber 52.

What is claimed is: 
     
       1. In an induction furnace for heating a lightguide preform and drawing a fiber therefrom, the furnace having a centrally located tubular susceptor surrounded by an insulating grain and an induction coil, comprising: a thin coating of the lightguide preform material on at least a portion of the inside surface of the susceptor; and   an insulating cylinder positioned about and spaced from the susceptor, interposed between the insulating grain and the susceptor wherein said cylinder substantially eliminates the migration of small particles of the grain to the preform and/or the fiber.   
     
     
       2. The furnace as set forth in claim 1, wherein: the thin coating material is silica; and   the susceptor is zirconium dioxide.   
     
     
       3. The furnace as set forth in claim 1, wherein: a silica soot is located between the cylinder and the susceptor.   
     
     
       4. The furnace as set forth in claim 3, wherein: a portion of the silica soot is consolidated on the outside surface of the susceptor.   
     
     
       5. The furnace as set forth in claim 3, wherein: a portion of the silica soot is consolidated on the inside surface of the cylinder.   
     
     
       6. A method of drawing a fiber from a lightguide preform, the method comprising the steps of: axially introducing the preform into a tubular susceptor within an induction furnace, said susceptor being surrounded by an insulating grain, said susceptor being further surrounded by and spaced from an insulating cylinder interposed between the grain and the susceptor, the susceptor having a coating of the preform material on at least a portion of the inside surface thereof; wherein said cylinder substantially eliminates the migration of small articles of the grain to the preform and/or the fiber;   activating high frequency induction coils to couple electromagnetic energy to the susceptor to elevate the temperature thereof to reflow a portion of the lightguide preform therein; and   drawing a fiber from the reflown portion of the preform.